A free, ad supported, version of the Periodic Table Explorer (contains all the same great information as the paid-for version!).
The Periodic Table Explorer contains more than 1400+ pages of content covering all the elements of the periodic table, their compounds, physical properties, isotopes, spectra, reactions and production/isolation information.
English pronunciations of every element available from the menu screen and data pages.
There are detailed biographies, a glossary, searchable compound and physical constant databases, molecular mass calculator and the ability to search the entire 1400 pages of content.